1. Field of the Invention
This invention relates to the field of generating three-dimensional graphics; more specifically, to the field of generating multiple resolutions of an object in a three-dimensional environment.
2. Background of the Invention
Realistic three-dimensional object rendering for use in games and other software applications has been the goal for software and hardware makers in the computer industry for years. However, numerous problems prevent the achievement of realistic three-dimensional object rendering on a typical user""s home computer.
Three-dimensional graphics use polygons to create the object to be rendered. These polygons are created and manipulated to portray curvature and details of the object. The more polygons used to create an object, the more detailed and realistic an object will appear. However, the more polygons used to create an object, the more computations required to render the object, thus slowing down the speed at which the object is rendered. Thus, there is a tradeoff from the developer""s standpoint between speed and realism.
The resolution of this problem is not easy. As most users do not have the latest, most powerfull personal computer, the developer must design the objects for the lowest common denominator if the developer wants to reach the greatest number of potential users for the product. Thus, the developer must assume the user""s processor is slow and is therefore capable of only rendering a small number of triangles per second. Therefore, the developer, when making the tradeoff described above, must favor the speed side of the equation, and design objects with fewer triangles than if faster machines were being used by all users. This solution, however, pleases neither the user with a low-end computer nor the user with the high-end computer. The user with the low-end computer will most likely still have images which are slow and choppy, because the developers are unwilling to completely sacrifice realism, and the user with a high-end computer will have images which appear artificial and robotic because the application is not designed to take advantage of the high-end machine""s greater processing power. In fact, on some high-end systems, the application will be too fast to play or interact with because the polygon count is too low.
Another problem facing the developer is the fact that the same object requires more detail when closer to the screen than it requires if it is in the background. When an object is closer to the screen, the angles and straight edges of the polygons comprising the object can be seen more clearly. At this point, more polygons are needed to smooth the angles and continue the realistic rendering of the object. However, the most detailed version of the object cannot always be used to render the object because the application will require too much computing power to quickly and smoothly render images on the screen. In order to achieve smooth 3D animation, the processor must render 3D objects at 20 to 60 frames per second. If too many polygons are used for each object, thus providing the necessary realism for the object when it is close to the screen, then the processor will not be able to achieve the above minimum frame rate required for smooth rendering.
One solution to allow realistic rendering of three-dimensional objects while also limiting the number of polygons on the screen is to use Level of Detail mapping. Level of Detail mapping provides different levels of resolutions of an object based upon the distance of the object to the screen. In order to create the different levels of detail, the developer must create different versions of the object for each level required. Typically, only three or four levels are used because storage of multiple versions of each object to be rendered can consume too much of the user""s system resources.
There are several drawbacks to the level of detail methodology. First, this method has a large impact on system resources, as described above. Each object now requires three or four times more storage space than previously required to store each version of the object. Each level requires a separate vertex list as well as a separate data structure. Second, when transitioning from one level to another, an effect known as object popping occurs. The higher detailed version of an object is abruptly rendered as the object moves towards the screen, and xe2x80x9cpopsxe2x80x9d out at the viewer, ruining the 3D immersive qualities of the application. The level of detail method also requires extra authoring of each version of the object, requiring more time from the developer. Level of Detail also does not address the lowest common denominator problem described above. The highest level of detail of each object must be created in consideration of the user with an inefficient computer who will be using the application. Thus, the highest level of detail cannot contain too many polygons or the image will appear slow and choppy on the low-end user""s computer. Again, this image will also appear angular and robotic on the high-end user""s computer, as it does not take advantage of the high-end computer""s greater processing power.
In accordance with the present invention, an apparatus, system, and method is disclosed for producing realistic rendering of a 3D object while minimizing the use of user system resources and maximizing fidelity without sacrificing speed. The invention produces a continuous level of detail of an object using vertex merging responsive to the location of the object on the screen and other factors, thus eliminating the object popping effect. As the object moves towards the background, and therefore requires less polygons in order to provide a realistic rendering, vertices of the object are merged together in a manner designed to cause the least visual distortion. As the vertices are merged, polygons within the object are eliminated, thus lowering the polygon count of the object continuously as it moves farther and farther away from the screen. As an object moves towards the screen, vertices are added to the object, adding polygons to the object and thus providing a more realistic representation of the object as it grows close to the user and fine details become necessary. Thus, at any given moment, every object on the screen only has as many polygons as is required to provide a realistic rendering of the object. No polygons are being unnecessarily drawn, and thus optimum use is being made of the user""s system. No object-popping effects are created as polygons are added or removed from the object on a continual basis based on the object""s movement in the 3D environment.
Additionally, the invention requires only one version of the object to be authored and stored on the user""s system, thus minimizing the impact on system resources. One vertex list is used which preferably specifies the highest level of detail, and the system in accordance with the present invention is able to then generate the continuous level of detail of the object for display on the screen. Also, the system advantageously increases and decreases the resolution of the objects on the fly. Thus, as only the current level of detail being displayed is stored, minimal use of memory is required. By storing certain minimum information which is determined prior to run-time to guide the resolution changes, the resolution changing is performed at run time at optimal speed. Another benefit of the present invention is its ability to allow a developer to tweak the vertex merging in accordance with the developer""s own preferences. Finally, the invention automatically adjusts the amount of polygons in a screen responsive to the capabilities of a user""s system, providing an optimal image for every user. In one embodiment, the invention monitors the system to determine the frame rate at which the frames are being rendered, and adjusts the total amount of polygons allowable on the screen at one time accordingly.
Additionally, a target frame rate may be set, which allows the user to specify the speed at which the scenes should be rendered. The present invention then dynamically adjusts the total amount of polygons to ensure the frame rate is maintained. Alternatively, the invention allows a polygon count to be specified, and then ensures that this amount of polygons is always on the screen, regardless of the frame rate.
In a preferred embodiment, a three-dimensional visual representation of an object having multiple resolutions is created by retrieving a vertex list for the object, determining a collapse order for the vertices identified in the vertex list, reordering the vertices identified in the vertex list responsive to the determined collapse order, and creating a vertex collapse list responsive to the collapse order, where the vertex collapse list specifies, for a target vertex, a neighbor vertex to collapse to. The vertex list may comprise 3D coordinates of vertices without referring to other vertex attributes or, in alternate embodiments, the vertex list may refer to other vertex attributes such as colors or normals.
More specifically, in a preferred embodiment, the collapse order of the object is determined by determining an optimal collapse path from the set of collapse paths, computing visual distortion factors for the selected collapse path, determining a collapse value for the selected collapse path, repeating for each path in the set of collapse paths, comparing the collapse values to determine a collapse path causing a least visual distortion to the object, selecting a next vertex to be collapsed, collapsing the object along the selected path, and repeating until a minimum resolution level is attained.